Definitions 2

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Boolean variable
May have two discrete possible values e.g. True or False
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Truth table
A table that expresses a Boolean output Q in terms of Boolean inputs X, Y, Z etc. to which one or more Boolean functions such as OR, AND and NOT, are applied
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Logic gate
An electronic circuit that performs a Boolean function
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De Morgan's Law
A+B=(A'.B')' and A.B=(A'+B')'
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Hardware
Electronic/ electrical circuits that a computer is assembled from. The platform on which the software executes
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Main memory
Memory that is directly addressable by the processor
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Memory location
A separately addressable area of main memory
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RAM
Random access memory; volatile main memory in which the locations can be accessed directly in any order with the same access time for all writing and reading operations
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ROM
Read only memory; non-volatile main memory that cannot be written to once it is set up
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EEPROM
Electrically erasable programmable read only memory; its contents may be altered but writing is about 100 times slower than reading
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Computer bus
A set of parallel wires connecting independent components of a computer system
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System bus or external bus
The main highway connecting the processor, main memory and I/O controllers; it is made up of a data bus, an address bus and a control bus
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I/O
Allows CPU to communicate with peripherals
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Data bus
Bidirectional bus typically consisting of 32 wires, used to transport data between the three components of the three box model
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Address bus
Unidirectional bus, typically consisting on 32 wires, used to address memory and I/O locations
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Control bus
Bidirectional bus, typically consisting of 8 wires, used to transport control signals between the three components of the three box model
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Clock signal (I/O)
For timing purposes
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Reset signal (I/O)
Used to initalise components
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Memory read signal (I/O)
Used to assert that the memory location currently in use is being read from
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Memory write signal (I/O)
Used to assert that the memory location currently in use is being written to
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I/O signal
Used to indicate that the processor wishes to use an I/O controller not main memory when I/O and main memory share memory addresses
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Peripheral
A computer device that is not a part of the CPU. It can be external (e.g. mouse, keyboard, printer, monitor, memory stick or scanner) or internal, such as a CD-ROM drive
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I/O device
A hardware unit that sends or receives data by communicating with the processor and main memory through an I/O controller
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I/O controller
An electronic circuit that connects to a system bus and an I/O device; it provides the correct voltages and currents for the system bus and the I/O device
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Secondary storage
Permanent storage memory not directly connected to the processor; also called backing store
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I/O port
Part of I/O controller processor uses to exchange data with a peripheral. Simply a set of data, commands and status registers
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Main memory address
A unique numeric code corresponding to a location in memory
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Stored program concept
Proposed by Jon von Neumann and Alan Turing 1945. A program must be resident in main memory to be executed; it is processed by fetching machine code instructions in sequence from main memory and executing them one at a time in the processor
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Von Neumann stored computer
The von Neumann computer has a single memory shared between program instructions and data and share a data bus. Instructions and data are fetched one at a time one after the other
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Harvard stored computer
The Harvard computer has separate instruction and data memories and have separate instruction and data buses. Instructions are fetched serially from the data memory and executed in the processor, when data is needed it is fetched from data memory
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Microcontroller
A complete computer (processor, memory, I/O) on a single chip
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Register
Very fast storage location inside the processor or I/O controller that can be written to and read from
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General purpose register
A register not assigned a specific tole by the processor designer. Programmers may use general purpose registers
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Dedicated register
A register assigned a specific role by the processor designer. Programmers may use some but not all dedicated registers
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Program control unit
Fetches program instructions from memory, decodes them and executes them one at a time
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Arithmetic and logic unit (ALU)
Performs arithmetic and logical operations on data such as addition and subtraction fixed point and floating point arithmetic; Boolean logic such as AND OR XOR and a range of shift operations
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Internal clock
Derived directly or indirectly from the system clock
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Internal bus
Several internal buses link the control unit, the ALU and the registers
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Stack pointer (SP)
Points to a stack holding return addresses, procedure or function parameters and local variables; it is accessed when a procedure or function is called or an interrupt is served
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Program counter (PC)
Points to the next instructions to be fetched and executed
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Status register (SR)
Holds condition codes to indicate the outcome of operations e.g. an arithmetic operation may produce a positive, negative zero or overflow result so a flag is set accordingly. Status information such as whether interrupts are enabled is in the SR
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Accumulator (ACC)
Holds the result of the current set of calculations e.g. ADD#36 means add 36 to the contents of the accumulator register and store results in the accumulator
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Current instruction register (CIR)
Holds the current instruction to be executed while it is decoded and executed
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Memory address register (MAR)
Holds the address of the memory location currently being accessed by the processor
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Memory buffer register (MBR)
Holds the data items being transferred to or from the memory locations currently being accesed by the processor
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Clock speed
Of a processor the frequency in megahertz or gigahertz at which the processor executes instructions
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Word length
The number of digits in a binary word
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Bus width
The number of signal wires or lines allocated to the bus
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System clock
A quartz controller oscillator that supplies a timing signal at a fixed rate
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Other cards in this set

Card 2

Front

A table that expresses a Boolean output Q in terms of Boolean inputs X, Y, Z etc. to which one or more Boolean functions such as OR, AND and NOT, are applied

Back

Truth table

Card 3

Front

An electronic circuit that performs a Boolean function

Back

Preview of the back of card 3

Card 4

Front

A+B=(A'.B')' and A.B=(A'+B')'

Back

Preview of the back of card 4

Card 5

Front

Electronic/ electrical circuits that a computer is assembled from. The platform on which the software executes

Back

Preview of the back of card 5
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